This invention relates to a phase shift circuit suited to be used with the amount of phase shift fixed to a predetermined value.
Since, in a circuitry incorporating a phase shift circuit and integrated on a semiconductor chip, values of resistance and capacitance of integrated resistors and capacitors become non-uniform by reason of production errors and particularly the resistance values vary with temperatures, the amount of phase shift by the phase shift circuit is also varied with the errors and/or the temperature dependent variations. Accordingly, it is desirable that the phase shift circuit integrated as such be used as a variable phase shift circuit which can externally be changed in phase shift amount. An example of this type of phase shift circuit, variable in phase shift amount, is disclosed in U.S. Pat. No. 4,306,198.
In the phase shift circuit described in this U.S. Pat. No. 4,306,198, the phase shift amount is made variable but it is in no way taken into consideration that the phase shift circuit may be used with the amount of phase shift fixed to a predetermined value. Thus, the prior art phase shift circuit is disadvantageous in that a predetermined amount of phase shift can not be obtained regardless of production errors and temperature variations. Further, the prior art phase shift circuit can not be manufactured as an integrated phase shift circuit for use at low frequencies because resistors and capacitors having large resistance and capacitance values are difficult to integrate.